Concrete is a composite material composed of a coarse granular material (known as aggregate or filler) embedded in a hard matrix of binder material (the cement or glue, e.g., Portland cement) that binds the aggregate and holds them together, at least partially filling the space around the aggregate. Concrete initially is formed as a semi-liquid slurry that cures to form a strong and hard rock-like structure. As a result, it can be poured in place and molded or otherwise formed into a variety of structural shapes. This formability and its strength makes concrete a versatile material that can be used in many different types of structures utilized in connection with construction projects including, not limited to, architectural structures, foundations, mortar, walls, pavement for highways and runways, parking structures, bridges, dams, pools, pipes, tanks, fences, poles, and even boats.
Concrete is not a new material having been used in construction for thousands of years. Many ancient Roman concrete structures survive today. The Roman Pantheon and the Coliseum are two prominent examples. Famous modern concrete structures include the Hoover Dam and the Panama Canal, both of which involved massive quantities of concrete, with concomitant problems.
Despite its long history, conventional concrete has many long-standing problems. One problem is the very high pH of uncured concrete, which can irritate or chemically burn a person's skin. Another problem is the short time that the uncured concrete remains workable before the curing process progresses to a point that precludes further working. Yet another problem is the heat produced, called “heat of hydration” by many in the cement industry. Heat of hydration is actually an exothermic reaction that occurs during the curing process in which, for example, the temperature of the curing concrete may rise by 17° C. to 108.9° C. (e.g., by 35° F. to 228° F.) or more above ambient temperature. This temperature increase results in thermal expansion of and/or interior stresses in the concrete, and may result in cracking and/or slab cud, and requires that lengths of the curing concrete be cut, and/or that cooling be provided, to mitigate problems resulting from the thermal expansion, particularly in larger volumes and thicknesses of poured concrete. Cutting presents another serious problem of its own since cutting generates significant quantities of silica-containing dust, which is known to be potentially carcinogenic and otherwise bad for the health of workers involved. Other problems include porosity resulting from water bleed-out during the curing process, which allows water and dissolved salts to enter the cured concrete, causing corrosion of reinforcing metal rebar embedded in the concrete and possible chipping and spalling due to freeze/thaw cycles.
Additionally, current concrete technology generally attempts, albeit unsuccessfully, to address thermal management of the major exotherms generated from the calcium hydroxide formation. The most widespread, but unsuccessful, techniques utilized include the use of industrial by-products reducing the Portland cement level and subsequently the heat generated as well as the use of external cooling. Major efforts are underway to cool mass pours of cement now in the Panama Canal project, Tappan Zee Bridge and many large dams. Cooling is still underway at the Hoover Dams built many years ago. Cooling methods include: aggregate cooling, sub-zero chillers (e.g., the four being used at the Tappan Zee Bridge project), dry ice, cooling pipes, and others. Many of these cooling devices add high costs and labor to construction costs. Often the cooling costs exceed the cost of cement in large mass pours. Without cooling, a run-away reaction can occur causing very high exotherms that generate temperatures approaching the boiling point of water. The attainment of high temperatures, for example in excess of 73.9° C. (16.5° F.), during curing generates ettringite crystal formation. These crystals create a cement product which is highly prone to failure after water exposure. Cooling is required to minimize this formation. Heat also generates expansion and subsequent cracking upon cooling. This shortens the life of many cement structures. Internal stresses are also formed from rapid heating and cooling found in construction today. These internal stresses reduce the service life of all structures built with a cement that has a high exotherm.
Another problem found today in concrete is the alkali-silica reaction (ASR). The ASR is a reaction which occurs over time in concrete between the cured, highly alkaline cement and reactive non-crystalline (amorphous) silica, which is found in many common aggregates. The ASR reaction, or more accurately the delayed ASR reaction (hereinafter referred to in shorthand as just “ASR”), is the same as the pozzolanic reaction, which is a simple acid-base reaction between calcium hydroxide, also known as Portlandite, or (Ca(OH)2), and silicic acid (H4SiO4, or Si(OH)4). This reaction can be schematically represented as following:Ca(OH)2+H4SiO4→Ca2++H2SiO42−+2H2O→CaH2.SiO4.2H2O
This reaction causes the expansion of the altered aggregate by the formation of a swelling gel of calcium silicate hydrate (C—S—H or CSH) within the cured concrete. This gel increases in volume with water and exerts an expansive pressure inside the solid concrete material, causing, among other things, internal stresses, spalling and loss of strength of the concrete, finally leading to its failure. ASR can cause serious expansion and cracking in concrete, resulting in critical structural problems that can even force the demolition of a particular structure. The mechanism of ASR causing the deterioration of concrete can be described in four steps as follows:                (1) The alkaline solution attacks the siliceous aggregate, converting viscous alkali silicate gel.        (2) Consumption of alkali by the reaction induces the dissolution of Ca2+ ions into the cement pore water.        (3) The penetrated alkaline solution converts the remaining siliceous minerals into bulky alkali silicate gel. The resultant expansive pressure is stored in the aggregate.        (4) The accumulated pressure cracks the aggregate and the surrounding cement paste when the pressure exceeds the tolerance of the aggregate.        
While not wishing to be bound to any one theory, those of skill in the art believe that this reaction also shortens the life of concrete. Typical concrete has a pH of 13.2 to 13.5. At pHs higher than 12.5, silicon dioxide the main component of sand and quartz will dissolve forming an alkali-silica gel. This gel expands and causes cracks and the causes the white discoloration in cement dividers that you often see in expressways. This obviously shortens their life. There was no way of stopping this formation. Additionally, saw-cutting into short lengths only minimizes the effect.
A variety of attempts have been made over the years to reduce, mitigate or otherwise avoid these long-standing problems with conventional concrete. To date, none of these attempts has succeeded in addressing each of these long-standing, well-known problems with conventional concrete.
A number of attempts have been made to address the issues raised above. For example U.S. Pat. No. 8,016,937 discloses various cementitious compositions in which the cementitious properties of fly-ash are carefully controlled. The compositions disclosed in this patent are targeted for: rapid setting, high early strength, and quick return to service applications where variable set times are desired. This patent further discloses the use of one or more materials selected from pH neutral activators, retarders, citric salts, accelerators, fly ash, air entraining agents, latex, borate salt compositions, kiln dust, furnace slag, scrubber ash, fibers, KOH, alkali metal activators, borates as strength gain retarders, MgOH, calcium aluminate, potassium citrate, wollastonite, potassium butylrate, water reducers, silica fume, MgO, boric acid, borax and/or aluminum sulfate. The properties disclosed in this patent include compositions having a two (2) hour compressive strength of greater than 3000 psi. While not wishing to be bound to any one advantage, it is believed that a minimum the compositions of the present invention are substantially free from one or more of pH neutral activators, retarders, citric salts, accelerators, fly ash, air entraining agents, latex, borate salt compositions, kiln dust, furnace slag, scrubber ash, fibers, KOH, alkali metal activators, borates as strength gain retarders, MgOH, calcium aluminate, potassium citrate, wollastonite, potassium butylrate, water reducers, silica fume, MgO, boric acid, borax and/or aluminum sulfate. Additionally, the compositions of the present invention are not designed to achieve, for example, rapid setting and/or a two hour strength of greater than 3000 psi.
U.S. Pat. No. 8,186,106 discloses the manufacture of high strength cement and mortar using industrial by-products where: (i) such products are targeted for general purpose applications including high strength and fast set applications; and/or (ii) the compositions further include one or more materials selected from pH neutral activators, retarders, citric salts, accelerators, fly ash, air entraining agents, latex, borate salt compositions, kiln dust, furnace slag, scrubber ash, fibers, KOH, alkali metal activators, borates as strength gain retarders, MgOH, calcium aluminate, potassium citrate, wollastonite, potassium butylrate, water reducers, silica fume, MgO, boric acid, borax, aluminum sulfate, shrinkage compensators, boric compounds, kaolin, sodium gluco-heptonate, lime kiln dust, cement kiln dust, scrubber ash, furnace slag, pozzolanic ash, organic retarders, activators, bottom ash, ground glass, recycled foundry sand, alkali metal activators, by-products and scrubber ash, wood ash, incinerator ash, zeolites, malic acid, glycolic acid, calcium nitrate, and/or malic, glycolic or calcium salts. While not wishing to be bound to any one advantage, it is believed that a minimum the compositions of the present invention are substantially free from all components listed in (ii) above. In addition, the compositions of the present invention are clearly not capable of the properties listed in (i) as a high exotherm is typically utilized in concrete products having both fast set and high strength properties.
U.S. Pat. No. 8,551,241 discloses lightweight compositions with high compressive strength and fast set. The disclosure contained therein discloses a diagram displaying an exotherm maximum temperature range from 63.3° C. to 108.9° C. (146° F. to 228° F.). Also FIG. 1 illustrates exotherm ranges from 58.9° C. to 74.4° C. (138° F. to 166° F.). FIGS. 3 through 9 of this patent clearly list an additional 30 exotherms displaying more cure curves of from the compositions of this invention. These range from 53.9° C. to 103.3° C. (129° F. to 218° F.). While not wishing to be bound to any one advantage, the compositions of the present invention yield cure curves that display very low exotherms of 0° C. to 16.6° C. (i.e., a change in temperature of 0° F. to 30° F.) from set temperature. On an average day of say about 21.1° C. (70° F.), the exotherm maximum temperature of the product might only reach 37.8° C. (100° F.). The compositions disclosed in U.S. Pat. No. 8,551,241 target compositions that achieve, in direct contrast to the compositions of the present invention, fast set times. The compositions of the present invention seek to achieve, and in do achieve, slow-set applications. This slow set enables an extended finishing time to the benefit of end users or applicators. Another point of distinction is that the formulations of the present invention do not seek to achieve a lightweight approach or benefit. This patent also further discloses the use of one or more materials selected from pH neutral activators, retarders, citric salts, accelerators, fly ash, air entraining agents, latex, borate salt compositions, kiln dust, furnace slag, scrubber ash, fibers, KOH, alkali metal activators, borates as strength gain retarders, MgOH, calcium aluminate, potassium citrate, wollastonite, potassium butylrate, water reducers, silica fume. MgO, boric acid, borax, aluminum sulfate, shrinkage compensators, boric compounds, kaolin, sodium gluco-heptonate, lime kiln dust, cement kiln dust, scrubber ash, furnace slag, pozzolanic ash, organic retarders, activators, bottom ash, ground glass, recycled foundry sand, alkali metal activators, by-products and scrubber ash, wood ash, incinerator ash, zeolites, malic acid, glycolic acid, calcium nitrate, and malic, glycolic or calcium salts. Additionally, this patent further discloses the use of one or more of LiOH, ground silica, sodium citrate, a wide range of di- and tri-citrate salts, gypsum, triethanol amine, phosphates, montmorillonite clay, diatomaceous earth, pumicite, high alumina content, sub-bituminous flyash, calcium aluminate, lightweight fillers, superplasticizers, foaming agents, viscosity modifying agents, coloring agents, pumice, pearlite, tuff, trans, rice husk, metakaolin, ground granulated blast furnace slag, CaCO3, added CaO—not already in concrete, hematite, magnetite, char, mullite, gehlenite, haematite, sillimatite, kyanite, adalusite, bauxite ore, limestone, calcium silicates, iron oxides, calcium ferrites, calcium alumino ferrites, TiO2, potassium tartarate, tartaric acid, malic acid, acetic acid, alkylsulphonates, alkylbenzyl fulfonates, alkylether sulphonate, oligomers, lightweight fillers, hollow spheres both ceramic and plastic, plastic beads, expanded clay and all materials listed in Tables, 4, 6, 8, 10, 12, 14, 15. In contrast the formulations of the present invention are substantially free from all components listed above.
Overall, adding by-products and residues from stone, metals, ceramics refining, grinding, smelting, furnace cleaning and the like only weaken a concrete composition/formulation. The intent of their usage is to reduce cement cost and/or reduce the exotherm by limiting the level of Portland cement in the composition. The only other option for contractors in mass pour applications is to utilize external mechanical cooling. This cooling often exceeds the concrete costs in mass pour jobs. In contrast, the present invention eliminates the need for external cooling through the utilization of advanced chemistry techniques. While not wishing to be bound to any one theory, it is believed that the reaction achieved as a result of the present invention results in a more efficient balanced equation, less by-product formation and higher strengths from higher CSH formation. A typical Phase I heat of hydration reaction only converts 50 percent of the calcium atoms to CSH. The reaction achieved by the present invention results in a much higher conversion to CSH minimizing the calcium hydroxide formation, minimizing the exotherm, and maximizing the strength (see, e.g., FIG. 9).
While not wishing to be bound to any one theory, or set of advantages, the various embodiments of the present invention offers solutions to both problems via an advanced chemical solution. The various embodiments of the present invention permit the realization of very low to no exotherms via in-situ calcium hydroxide conversion into more, or a higher concentration, of CSH (calcium silicate hydroxide), the glue of concrete. This occurs by converting the CSH into another molecule before it precipitates out of solution, so that no exotherm, or a very low exotherm, occurs. By staying below 73.9° C. (165° F.), and in some cases well below 73.9° C. (165° F.), the potential for ettrigite formation is eliminated. A beneficial additional aspect of this conversion is a significantly reduced calcium hydroxide level and a much reduced pH that accompanies it, (a pH of 11 to 12 versus a pH of 13, or even 13-plus). This correlates to a 10 fold to a 100 fold reduction in hydroxide formation. This lower pH eliminates the potential for ASR occurrence. As such, the present invention through the utilization of advanced applied chemistry represents a significant improvement in cement and building technology today by elimination of various problems that have been, for some time, vexing the cement/concrete industry.